1. Field of the Invention
The present invention relates to a hydrostatic transaxle apparatus, especially, for a vehicle having a vertical crankshaft engine.
2. Background Art
A hydrostatic transaxle apparatus called an IHT comprises a hydrostatic transmission (hereinafter, referred to as an xe2x80x9cHSTxe2x80x9d), an axle and a drive train interposed between the HST and the axle disposed together in a common housing. Some of various IHTs are used for a vehicle having a vertical crankshaft engine, wherein the rotary axis of the hydraulic pump of the HST must be disposed vertically, i.e., in perpendicular to the horizontal axle. If the rotary axis of the hydraulic motor of the HST is disposed horizontally, the drive train between the HST and the axle can be simplified. However, the configuration of a center section for fluidly connecting the hydraulic pump and motor to each other must be complicated. Further, output means such as a motor shaft of the hydraulic motor must be extended horizontally, thereby expanding the IHT in the horizontal direction.
In order to reduce the horizontal size of the IHT for a vertical crankshaft engine, and to simplify the center section of the HST, it is noticed that the rotary axis of the hydraulic motor may be disposed vertically. U.S. Pat. No. 4,979,583 discloses an IHT, wherein a hydraulic pump and a hydraulic motor are disposed vertically oppositely to each other so as to arrange both the rotary axes thereof vertically coaxially to each other.
The hydraulic pump and motor of U.S. Pat. No. ""583 are of a radial piston type. That is, each of them comprises a rotor serving as a cylinder block, and pistons inserted in the rotor so as to reciprocate radially (horizontally). In the hydraulic pump, a cam ring (track ring) is provided around the rotor. The cam ring is equal to a movable swash plate of an axial piston type hydraulic pump. A track ring is also disposed around the rotor of the hydraulic motor, in place of a swash plate of an axial piston type hydraulic motor. Both the rotors are rotatably provided around a vertically axial common pintle. Oil passages are formed within the pintle so as to constitute a closed circuit between the hydraulic pump and motor. Also, a horizontally plain plate is disposed around the pintle so as to be sandwiched between the hydraulic pump and motor, thereby guiding the cam ring.
The disclosed HST is axially (vertically) short, however, still radially (horizontally) expanded because the track rings must be disposed concentrically with the respective rotors and the pistons must be allowed to reciprocate radially. This is an obstacle to minimization of the IHT in the radial direction of the HST. Further, for positioning the rotors and track rings, the plate to be sandwiched between the hydraulic pump and motor must be provided around the pintle, thereby increasing the number of parts and costs. If the HST was comprised of an axial piston type hydraulic pump and motor, a single member of the name of a center section could be used for fluidal connection of the hydraulic pump and motor and for positioning the hydraulic pump and motor.
An object of the present invention is to provide a greatly minimized hydrostatic transaxle apparatus which may especially serve as an IHT for a vehicle having a vertical crankshaft engine, wherein a simple and economical configuration of an HST is secured. The hydrostatic transaxle apparatus comprises a housing filled therein with fluid so as to serve as a fluid sump, an axle disposed in the housing, a hydraulic pump disposed in the housing to be drivingly connected to a prime mover, a hydraulic motor disposed in the housing to be drivingly connected to the axle, and a center section disposed in the housing to fluidly connect the hydraulic pump and motor to each other.
To achieve the object, according to the present invention, the center section is disposed adjacently to the axle. The center section includes a pump mounting surface and a motor mounting surface in parallel to each other, onto which the hydraulic pump and the hydraulic motor are mounted respectively. A common axis penetrates the center section through both the pump mounting surface and the motor mounting surface so as to be disposed substantially perpendicularly to a longitudinal direction of the axle. Both rotary axes of the hydraulic pump and motor coincide with the common axis.
The axle is usually disposed horizontally. Thus, if the hydrostatic transaxle apparatus is adapted for a vehicle having a vertical crankshaft engine, the common axis and the rotary axes of the hydraulic pump and motor may preferably be vertical.
Accordingly, while the hydraulic pump and motor are disposed coaxially (preferably, vertically oppositely) to each other, the center section, which may be constituted by a single member, is used for fluidly connecting the hydraulic pump and motor, moreover for positioning the hydraulic pump and motor, thereby reducing the number of parts and costs.
The hydraulic pump and motor may be constituted by axial piston type hydraulic pump and motor, which are radially small. If the axle is disposed horizontally and the coaxial axes of the hydraulic pump and motor vertically, the hydrostatic transaxle apparatus can be horizontally minimized.
A pump shaft may serve as the rotary axis of the hydraulic pump, and the pump shaft may project outward from the housing so as to be fixedly provided thereon with a cooling fan. Preferably, most of the hydrostatic transaxle apparatus except the axle is disposed in an area of the rotary locus of the cooling fan when viewed along the pump shaft so as to minimize the size of the hydrostatic transaxle apparatus in the radial direction of the hydraulic pump and motor.
If the hydrostatic transaxle apparatus is comprised of a differential gear unit which differentially connects a pair of axles to each other, the center section adjacent to the axle may be also disposed adjacently to the differential unit. Correspondingly, the housing may comprise a pair of first portions for housing the respective axles, a second portion disposed between the first portions so as to house the differential unit, and a third portion interposed between one of the first portions and the second portion for housing the hydraulic pump and motor, wherein the center section is disposed substantially at the center of the third housing portion. In this case, the second and third portions of the housing are preferably disposed almost within the above-mentioned area of the rotary locus of the cooling fan.
While the pump shaft serves as the rotary axis of the hydraulic pump, a motor shaft may serve as the rotary axis of the hydraulic motor, and a common hole whose axis serves as the common axis may penetrate the center section through both the pump and motor mounting surfaces. In this case, the pump and motor shafts are inserted into the common hole. Assuming each of the pump and motor shafts has a first end surface and a second end surface, the first end surfaces are disposed in the common hole so as to face each other. The pump and motor shafts are extended oppositely to each other from the respective first end surfaces to the respective second end surfaces. If the pump and motor shafts are disposed vertically, the second end surfaces thereof define the top and bottom end surfaces of the HST.
In this arrangement, the axle may be disposed between a pair of parallel surfaces in which the second end surfaces of both the pump shaft and motor shaft are disposed respectively. Consequently, the axle and the HST are not offset from each other in the direction of the pump and motor shafts, thereby reducing the size of the hydrostatic transaxle apparatus in the same direction. If the pump and motor shafts are vertical, the vertical size of the hydrostatic transaxle apparatus can be reduced.
Furthermore, the axle may be disposed between a pair of parallel surfaces in which the first and second end surfaces of the motor shaft are disposed respectively. Thus, the axle can approach the motor shaft so as to secure a nice power transmission efficiency and a compact drive train therebetween. Further, if the motor shaft is disposed vertically and under the pump shaft, the height of the axle can be desirably lowered.
To prevent the pump and motor shafts from impeding each other in rotation, the common hole of the center section is shaped so as to separate the first end surfaces of the pump and motor shafts therein from each other.
The center section may be formed with a charge suction port for supplying fluid from the housing into the fluid circuit within the center section, and a partition wall may be provided to separate the charge suction port from the hydraulic pump and motor mounted on the center section. Therefore, impurities caused by operation of the HST can be prevented from being absorbed into the charge suction port.
The center section may be separably secured in the housing, thereby facilitating maintenance of the HST.
The housing may be constituted by a pair of first and second housing members joined to each other through a joint surface along a longitudinal direction of the axle, wherein the hydraulic pump may be disposed in the first housing member, and the hydraulic motor may be disposed in the second housing member, thereby facilitating maintenance of the interior parts of the hydrostatic transaxle apparatus. In this configuration, the center section may be separably secured with the first housing member so as to be laid between the hydraulic pump and the hydraulic motor in the housing along the joint surface.
A counter shaft may be provided for transmitting output force of the hydraulic motor to the axle. The counter shaft may be interposed between the motor shaft and the differential unit.
As an aspect for rotatably supporting the counter shaft, a support member which is separate from the housing may be fixed in the housing, thereby simplifying the housing out of consideration of journalling the counter shaft.
One side surface of the support member may be used for controlling a brake for braking the counter shaft, thereby reducing the number of parts for the brake. As one aspect thereof, a brake rotor is fixed on the counter shaft so as to be pressed against the one side surface of the support member.
A plurality of the support members may serve as the support member. One of the support members may be formed so as to retain a motor swash plate of the axial piston type hydraulic motor on an input side of the counter shaft, thereby reducing the number of parts.
Alternatively, a retainer for retaining the motor swash plate may be provided separately from the housing or the support member. The retainer may be separably secured with the housing, or with either the first or second housing member. Alternatively, the retainer may be fixed to the center section. Regardless, the housing, or one of the first and second housing members can be simplified in comparison with that and is formed so as to retain the motor swash plate.
For transmitting power from the motor shaft to the axle, a bevel gear or a face gear may be used.
Further, a control shaft rotatably supported by the housing for controlling the capacity and oil discharging direction of the hydraulic pump may be disposed in parallel to the counter shaft so that the control shaft and the counter shaft may be juxtaposed on a surface along the common axis penetrating the center section. This further reduces the size of the hydrostatic transaxle apparatus in the radial direction of the HST.
In order to reduce the size and costs of a hydrostatic transaxle apparatus, a second object of the present invention is to provide a compact and economic HST comprising hydraulic pump and motor. A center section incorporates a pair of oil passages for fluidly connecting the hydraulic pump and motor to each other, a simplified oil-charge valve structure for supplying the pair of oil passages with hydraulic oil, and a simplified oil-draining structure for draining oil from the pair of oil passages while a vehicle having the hydrostatic transaxle apparatus being drafted.
To achieve the object, a check valve for supplying the pair of oil passages in the center section with hydraulic oil is also used as a member for draining oil from the oil passages. Therefore, the number of components for constituting a valve for draining oil from the oil passages, which is separate from the check valve for oil-supply, are canceled so as to contribute for reducing the size and costs of the center section. Moreover, it resolves the dimensional dispersion of the components of the separate oil-draining valve causing the wrong performance of oil draining.
For constituting this valve, a pair of valve casings, each of which incorporates a valve member such as a ball or the like, are inserted into the center section so as to be rotatable around substantially horizontal axes thereof. The valve casings are turned over simultaneously, thereby being selectively put into either a charge (oil supply) mode or a drain mode. In the charge mode, a valve seat in each valve casing is arranged under the valve member so that the valve member in the higher-pressured oil passage is put on the valve seat and the other valve member in the lower-pressured oil passage is separated from the valve seat by the pressure of oil flowing into the center section from the oil sump in a housing incorporating the center section. In the drain mode, the valve seat in each valve casing is set above the valve member so that the valve member is constantly separated from the valve seat, thereby enabling the pressured oil in the center section to flow out into the oil sump in the housing.
An outer end portion of the valve casing, which projects outward from the housing, is formed with a fitting portion fitting a tool for rotating the valve casing, e.g., a slot into which a tip of a screwdriver is inserted. Accordingly, the rotation of the valve casing for switching its mode can be easily operated from the outside of the housing.
The outer end portion of the valve casing is partly cut away so as to set the valve casing into a position corresponding to one of the two modes. A spring member is pressured against the outer end portion of the valve casing. When setting one mode, the spring member is pressured against the cut-away surface so as to locate the valve casing. When setting the other mode, the spring member is pushed and raised by a side of the valve casing opposite to the cut-away surface.